CN112113584A

CN112113584A - Measuring device

Info

Publication number: CN112113584A
Application number: CN201911261739.7A
Authority: CN
Inventors: B·格莱希; J·拉米尔
Original assignee: Koninklijke Philips NV
Current assignee: Koninklijke Philips NV
Priority date: 2018-06-20
Filing date: 2019-12-10
Publication date: 2020-12-22
Anticipated expiration: 2039-12-10
Also published as: CN112107364A; CN114269233A; US11598677B2; JP7507795B2; US20200400509A1; AU2019451287A1; CN112384134B; WO2019243098A1; EP3583896A1; US20200397510A1; US11592341B2; US12007291B2; CA3104001A1; US20240264008A1; EP3986271A1; EP3986264A1; JP7407582B2; US11976985B2; AU2019290959A1; BR112021025765A2

Abstract

The invention relates to a measuring device (1) comprising a rotatable magnetic body (4) which can oscillate at a resonance frequency when excited by an external magnetic moment. The measurement device (1) is adapted to relate the resonance frequency to temperature or another physical or chemical quantity, such as pressure, in order to allow a wireless temperature measurement or a wireless measurement of another physical or chemical quantity via an external magnetic field providing an external magnetic moment. The measuring device may be relatively small, readable over a relatively large distance, and allow very accurate measurements to be made.

Description

Measuring device

Technical Field

The present invention relates to a measuring device and reading system for measuring temperature or other physical or chemical quantities such as pressure. The invention also relates to a kit of measuring devices as well as a measuring method and a computer program for measuring temperature or other physical or chemical quantities.

Background

Particularly during interventional procedures, it is often desirable to accurately determine, for example, the temperature of a certain tissue portion of the subject (e.g., the temperature of a tumor), or to accurately account for the effects of temperature changes on the measurement of another physical or chemical quantity (e.g., pressure). However, in many cases, the desired and often also required accuracy cannot be provided.

Disclosure of Invention

It is an object of the present invention to provide a measuring device and a reading system which allow an accurate determination of temperature or another physical or chemical quantity, such as pressure. It is a further object of the invention to provide a kit of measurement devices and to provide a measurement method and a computer program for measuring temperature or other physical or chemical quantities.

In a first aspect of the present invention a measuring device is presented, wherein the measuring device comprises:

-a housing for the housing,

a magnetic object arranged within the housing such that the magnetic object is rotatable out of an equilibrium orientation with an external magnetic moment acting on the magnetic object,

a reset torque unit adapted to provide a reset torque to force the magnetic object back into the equilibrium orientation in case the external magnetic moment has rotated the magnetic object out of the equilibrium orientation, so as to allow the magnetic object to rotationally oscillate at the resonance frequency excited by the external magnetic moment, and

a measuring element adapted to alter the resonance frequency in dependence of a) a temperature and/or b) another physical or chemical quantity, wherein, if the measuring element is adapted to alter the resonance frequency in dependence of the other physical or chemical quantity, the measuring device comprises a compensation element adapted to alter the resonance frequency in a first frequency direction in dependence of a temperature change, and if the compensation element is not part of the measuring device, the measuring device will alter the resonance frequency in a second frequency direction in dependence of the temperature change, the first frequency direction being opposite to the second frequency direction.

Thus, to measure temperature, the resonant frequency may be modified as a function of temperature using a measurement element. Thus, the temperature may be measured by determining the resonance frequency of the magnetic object, wherein a magnetic field may be generated which provides a magnetic moment for rotating the magnetic object out of its equilibrium orientation and for thereby exciting a rotational oscillation of the magnetic object such that it oscillates at the resonance frequency and generating an induced signal caused by the rotational oscillation of the magnetic object. The temperature may then be determined based on the generated sensing signal. In particular, magnetic fields with different excitation frequencies may be generated, wherein the resonance frequency may be determined as the excitation frequency at which the induction signal is optimized, wherein the determined resonance frequency may be used to determine the temperature based on a known distribution between the resonance frequency and the temperature. This allows a very accurate determination of the temperature.

Furthermore, if the measuring element is adapted to alter the resonance frequency in dependence on other physical or chemical quantities (e.g. pressure), the resonance frequency may in this case also be determined by using a magnetic field which provides a magnetic moment of the magnetic object for rotating the measuring device and by using the generated induction signal, wherein the determined resonance frequency is indicative of the other physical or chemical quantities. Here, a known division between the resonance frequency and other physical or chemical quantities may be used. Furthermore, since the measuring device comprises a compensating element adapted to modify the resonance frequency in a first frequency direction in dependence of a temperature change, the measuring device will modify the resonance frequency in a second frequency direction in dependence of the temperature change if the compensating element is not part of the measuring device, the first frequency direction being opposite to the second frequency direction, in which case a temperature-induced shift of the resonance frequency, which is undesired, can be reduced or even eliminated. The first frequency direction is a direction towards higher or lower frequencies and the opposite second frequency direction is a direction towards lower or higher frequencies.

The measuring element is preferably an additional element present in addition to the housing, the magnetic body and the restoring torque unit. It can be a single element or a combination of several sub-elements. The measuring element may comprise, for example, one or more magnetic materials, which change its magnetization as a function of temperature, and if the measuring element should be adapted to measure temperature, it may be arranged within the measuring device such that the resonance frequency changes with temperature. However, if the measuring device should be used for measuring other physical or chemical quantities, these magnetic materials may also be selected and arranged such that they compensate for an undesired temperature dependence of the resonance frequency of the measuring device, in order to make the resonance frequency of the measuring device temperature-independent.

Note that the term "external magnetic moment" refers to a magnetic moment caused by an external magnetic field providing unit located outside the measurement device. Preferably, if the measurement device is arranged inside the subject, the magnetic field providing unit is also located outside the subject.

Preferably, the return torque unit comprises a further magnetic object for generating a magnetic field at the location of the magnetic object such that it provides the return torque and/or a torsion spring mechanism for providing the return torque. In one embodiment, a magnetic object is attached to one end of a filament, wherein the other end of the filament is attached to a housing, the filament adapted to prevent the magnetic object from touching another magnetic object due to its magnetic attraction to allow the magnetic object to rotationally oscillate. The further magnetic object is preferably fixedly attached to the housing. However, the further magnetic object may also be arranged within the housing such that it can oscillate rotationally with respect to the housing. In particular, another magnetic object may be attached to one end of the filament, wherein the other end of the filament may be attached to the housing. In one embodiment, the further magnetic object is rotatable around a virtual rotation axis passing centrally through the further magnetic object, wherein the further magnetic object is rotationally symmetric about the virtual rotation axis. The magnetic object and/or the further magnetic object may be a sphere and/or a magnetic cylinder. The virtual axis of the magnetic object and the virtual axis of the further magnetic object are preferably aligned with each other.

These techniques allow to provide a reset torque and thus a rotational oscillation of the magnetic object, so that the measuring device may be relatively small, the resonance frequency of the measuring device may be provided as a function of temperature or as a function of other physical or chemical quantities as desired, and the structure of the measuring device may still be relatively simple.

In one embodiment, the measuring device is adapted such that the further magnetic object is rotatable out of the equilibrium orientation if the external magnetic moment acts on the further magnetic object, wherein the reset torque unit is adapted to also provide a reset torque to force the further magnetic object back into the equilibrium orientation if the external magnetic moment has rotated the further magnetic object out of the equilibrium orientation in order to allow the further magnetic object to be excited by the external magnetic moment into a rotational oscillation, wherein the rotational oscillations of the magnetic object and the further magnetic object have the same resonance frequency and a phase difference of 180 degrees. This reduces (optimally even eliminates) the torque on the housing. The reset torque unit may use a magnetic object to provide a reset force to another magnetic object. In particular, in one embodiment, the magnetic object forms a first magnetic dipole, the further magnetic object forms a second magnetic dipole, and the magnetic object and the further magnetic object are arranged such that in the equilibrium orientation the first magnetic dipole and the second magnetic dipole point in opposite directions. In one embodiment, the magnetic object and the further magnetic object are directly connected to each other via a torsion spring, so that in this case the return torque unit comprises a torsion spring.

Preferably, the magnetic object and/or the further magnetic object is a permanent magnet. Furthermore, the housing is preferably cylindrical. If the housing is cylindrical, it can be introduced into a tubular medical device (e.g., a guidewire) with relative ease.

Preferably, the measuring means is adapted to fulfil at least one condition from the list comprising i) a Q factor of at least 100, ii) at least 0.5 μ Am²And iii) a resonance frequency of at least 100 Hz. It has been found that the accuracy of determining the temperature or other physical or chemical quantity can be further improved if at least one of these conditions is met.

It is further preferred that the measuring means is radiopaque. This allows the measurement device to be visualized by using an X-ray imaging system, such as a computed tomography system, an X-ray fluoroscopy system, an X-ray C-arm system, etc.

Preferably, the measuring element is adapted such that the strength of the magnetic field generated at the location of the magnetic object and/or the dipole moment of the magnetic object changes with a) temperature and/or b) other physical or chemical quantities. By varying the strength of the magnetic field generated at the location of the magnetic object and/or the dipole moment of the magnetic object with a change in temperature and/or with a change in other physical or chemical quantities, the resonance frequency can be varied in a technically relatively simple manner as a function of temperature and/or other physical or chemical quantities.

In one embodiment, the measuring element comprises a magnetic material influencing the magnetic field generated by the further magnetic object, wherein the influence of the magnetic material is temperature dependent in order to change the magnetic field strength at the location of the magnetic object in case of a temperature change. The magnetic material may be arranged adjacent to another magnetic object. It may be adapted such that its magnetization decreases with increasing temperature. Furthermore, it may be selected and arranged such that its magnetization direction is opposite to the magnetization direction of the further magnetic object. However, it may also be chosen and arranged such that its magnetization direction is the same as the magnetization direction of another magnetic object. The magnetic material is preferably a soft magnetic material. By using such a magnetic material, the resonance frequency can be modified very precisely as a function of temperature in a technically very simple manner without requiring too much space.

In a preferred embodiment, the measuring element is adapted such that if the temperature changes and/or if other physical or chemical quantities change, the distance between the magnetic object and the other magnetic object changes in order to change the magnetic field strength at the location of the magnetic object. In one embodiment, the further physical or chemical quantity is a pressure, wherein the measuring element comprises a flexible portion of a wall of the housing, wherein the magnetic object or the further magnetic object is attached to the flexible portion such that an external pressure from outside the housing acting on the flexible portion causes a change of the distance between the magnetic object and the further magnetic object.

In one embodiment, the measuring element comprises a steam bed on which a further magnetic body is arranged, wherein the size of the steam bed and thus the distance between the magnetic body and the further magnetic body varies with the temperature. In another embodiment, the measuring element comprises a lever structure via which the magnetic object is attached to the housing, wherein the lever structure comprises a material which changes its length as a function of temperature such that the distance between the magnetic object and the further magnetic object changes with temperature. These techniques also allow to provide the temperature dependence of the resonance frequency very accurately.

In one embodiment, the measuring element comprises a magnetic material which is applied to the magnetic object and influences the dipole moment of the magnetic object, wherein the influence of the magnetic material is temperature dependent in order to change the dipole moment of the magnetic object if the temperature changes.

Preferably, the compensation element comprises a magnetic material which changes its magnetization and thereby the resonance frequency as a function of temperature, wherein the magnetic material is selected and arranged within the measuring device such that the direction of change of the resonance frequency is the first frequency direction. The compensating magnetic material is preferably arranged adjacent to the magnetic object and/or adjacent to another magnetic object. This also allows the measuring device to be designed such that the detrimental temperature dependency can be significantly reduced or even eliminated in a technically relatively simple manner and without requiring a large amount of space within the housing.

In another aspect of the invention, a kit of a plurality of measuring devices is proposed, wherein each measuring device is adapted to have a resonance frequency in a respective frequency range when the respective measuring device is used for making measurements, wherein the frequency ranges of the different measuring devices do not overlap. By using a kit of these multiple measuring devices, measurements of e.g. temperature and/or other physical or chemical quantities can be made simultaneously, wherein these measurements can still be distinguished.

In one aspect of the present invention a reading system for reading a measuring device is presented, wherein the reading system comprises:

an excitation and induction signal unit adapted to a) generate a magnetic field providing a magnetic moment for rotating the magnetic object of the measuring apparatus out of its equilibrium orientation and for thereby exciting a rotational oscillation of the magnetic object such that it oscillates at a resonance frequency, and b) generate an induction signal caused by the rotational oscillation of the magnetic object,

a determination unit adapted to determine a temperature or other physical or chemical quantity based on the generated sensing signal.

In another aspect of the present invention, a measurement method for performing measurement by using a measurement apparatus is presented, wherein the measurement method comprises:

generating a magnetic field providing a magnetic moment for rotating the magnetic object of the measuring device out of its equilibrium orientation and for thereby exciting a rotational oscillation of the magnetic object such that it oscillates at a resonance frequency and generating an induced signal caused by the rotational oscillation of the magnetic object,

-determining a temperature or other physical or chemical quantity based on the generated sensing signal.

In a further aspect of the invention a computer program is presented comprising program code means for causing a reading system according to claim 13 to carry out the steps of the measuring method according to claim 14, when the computer program is run on a computer controlling the reading system.

It shall be understood that the measurement device according to claim 1, the kit of measurement devices according to claim 12, the reading system according to claim 13, the measurement method according to claim 14 and the computer program according to claim 15 have similar and/or identical preferred embodiments, in particular as described in the dependent claims.

It shall be understood that preferred embodiments of the invention may also be any combination of the dependent claims or the above embodiments with the respective independent claims.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

Drawings

In the following drawings:

figure 1 shows schematically and exemplarily an embodiment of a measuring device for measuring pressure,

figure 2 shows schematically and exemplarily a further embodiment of a measuring device for measuring a temperature,

figure 3 shows schematically and exemplarily a further embodiment of a measuring device for measuring a temperature,

FIG. 4 shows schematically and exemplarily an embodiment of a reading system for reading a measuring device, an

Fig. 5 shows a flow chart exemplarily illustrating an embodiment of a measuring method for measuring a temperature or another physical or chemical quantity.

Detailed Description

Fig. 1 shows schematically and exemplarily an embodiment of a measuring device. The measuring device 1 comprises a housing 2 and a magnetic object 4, which magnetic object 4 is arranged within the housing 2 such that it can be rotated out of an equilibrium orientation if an external magnetic moment acts on the magnetic object 4. The marking device 1 further comprises a reset torque unit 3 adapted to provide a reset torque in case an external magnetic force has rotated the magnetic object 4 out of the equilibrium orientation to force the magnetic object 4 back into the equilibrium orientation in order to allow the magnetic object 4 to rotationally oscillate by external magnetic moment excitation. In this embodiment, the housing 2 is cylindrical and the magnetic object 4 is rotatable about a virtual axis of rotation centrally through the magnetic object 4, wherein the magnetic object 4 is rotationally symmetric about the virtual axis of rotation. In particular, in this embodiment, the magnetic object 4 is a magnetic sphere.

The reset torque unit 3 comprises a further magnetic body 3 for providing a reset torque. In particular, the magnetic object 4 is attached to one end of the filament 7, wherein the other end of the filament 7 is attached to the housing 2. The thread 7 is adapted to prevent the magnetic object 4 from touching the other magnetic object 3 due to their magnetic attraction and to allow the magnetic object 4 to oscillate in rotation. In this embodiment, the further magnetic object 3 is fixedly attached to the housing 2 by using glue 9.

The magnetic object 4 forms a first magnetic dipole, the further magnetic object 3 forms a second magnetic dipole, and the magnetic object 4 and the further magnetic object 3 are arranged such that in the equilibrium orientation the first dipole and the second dipole point in opposite directions. Preferably, the first magnetic body 4 and the second magnetic body 3 are permanent magnets, wherein in the equilibrium orientation the north pole of the magnetic body 4 faces the south pole of the other magnetic body 3 and vice versa.

The housing 2 is cylindrical, wherein the cylindrical housing 2 comprises two end faces 30, 31, and the further magnetic object 3 is fixedly attached to the first end face 30, and the end of the filament 7 opposite to the end attached to the magnetic object 4 is attached to the second end face 31 of the cylindrical housing 2.

In this embodiment, the second end face 31 of the housing 2 is formed by the flexible portion 8 of the wall of the housing 2, wherein the magnetic object 4 is attached to the flexible portion 8 via the filament 7 such that an external pressure acting on the flexible portion 8 from outside the housing 2 causes a change in the distance between the magnetic object 4 and the further magnetic object 3. This change in distance due to the external pressure results in a change in the magnetic field strength generated by the further magnetic object 3 at the location of the magnetic object 4 and thus in a change in the resonance frequency. Therefore, the resonance frequency is changed in accordance with the external pressure, so that the measuring apparatus 1 can be used to measure the external pressure as another physical quantity. Thus, the flexible portion 8 of the wall of the housing 2 can be seen as a measuring element, which is adapted to alter the resonance frequency in dependence of the external pressure.

The measuring device 1 further comprises

magnetic material

5, 6 arranged adjacent to the further magnetic object 3. The

magnetic material

5, 6 influences the magnetic field generated by the further magnetic object 3, wherein the influence of the

magnetic material

5, 6 is temperature dependent in order to change the magnetic field strength at the location of the magnetic object 4 and thus the resonance frequency in case of a temperature change. The

magnetic material

5, 6 is adapted such that its magnetization decreases with increasing temperature. Further, the magnetic material 6 is adapted such that its magnetization direction is opposite to that of the other magnetic object 3, and the magnetic material 5 is adapted such that its magnetization direction is the same as that of the other magnetic object 3. The

magnetic materials

5, 6, which are soft magnetic materials, thus influence the resonance frequency in opposite frequency directions depending on the temperature, i.e. one of these magnetic materials causes a change towards higher frequencies with increasing temperature, while the other one of these magnetic materials causes a change towards lower frequencies with increasing temperature.

In this embodiment, the measuring device should be used for measuring pressure, so that the resonance frequency should not be temperature dependent. However, for example, the flexible portion 8 of the housing wall, which may be formed by a film, may have a temperature-dependent flexibility, so that the resonance frequency may generally also be temperature-dependent. Other parts of the measuring device may also be temperature dependent, wherein this dependence may also affect the resonance frequency. To compensate for this unwanted temperature dependent frequency shift, the

magnetic materials

5, 6 can be tailored such that they provide the same frequency shift in opposite frequency directions depending on the temperature change. In particular, the

magnetic materials

5, 6 may be selected and arranged such that any temperature dependence of the resonance frequency of the measuring device 1 is cancelled out. It is also possible to use only one of the magnetic materials, i.e. only the magnetic material that decreases the resonance frequency with increasing temperature or only the material that increases the resonance frequency with increasing temperature, to reduce or even eliminate the temperature dependence of the resonance frequency of the measuring device 1.

In another embodiment the second end face 31 does not comprise a flexible part 8 but is rigid and a soft magnetic material is applied to enhance the temperature dependence of the resonance frequency for temperature measurement using the measuring device. Also in this embodiment, only one of the magnetic materials may be used, which shifts the resonance frequency in the opposite direction according to the temperature change. In particular, in this embodiment, preferably only a magnetic material 6 is used, which has a magnetization direction aligned with the magnetization direction of the further magnetic object 3.

If the measuring device is used for measuring temperature, the

magnetic material

5, 6 can be considered as a measuring element adapted to modify the resonance frequency in dependence of the temperature. If the measuring device is used for measuring pressure, the flexible portion 8 of the wall of the housing 2 is considered as a measuring element adapted to modify the resonance frequency in dependence of the pressure, and the magnetic material 6 is considered as a compensating element adapted to modify the resonance frequency in dependence of the temperature change in a first frequency direction, which is opposite to a second frequency direction, in dependence of the temperature change if the compensating element 6 is not part of the measuring device.

Fig. 2 shows schematically and exemplarily a further embodiment of the measuring device. The measuring device 101 is adapted to measure a temperature, wherein in this embodiment the measuring element comprises a steam bed 113 on which the further magnetic body 103 is positioned, the size of the steam bed 113 and thus the distance between the rotating magnetic body 104 and the further magnetic body 103 varying with the temperature. Also in this embodiment, the measurement device 101 comprises a housing 102, and the magnetic object 104 is arranged within the housing 102 such that it can be rotated out of an equilibrium orientation if an external magnetic moment acts on the magnetic object 104. Further, also in this embodiment, the magnetic substance 104 is attached to the end face of the housing 102 via the filament 107. The reset torque is provided by the further magnetic object 103, wherein, similar to the embodiment described above with reference to fig. 1, in the equilibrium orientation of the rotatable magnetic object 104, the magnetic dipole of the magnetic object 104 is directed in the opposite direction to the magnetic dipole of the further magnetic object 103. The vapor bed 113 includes the membrane 110, vapor 111, and liquid 112 that can be adsorbed to a solid material. If the temperature changes, the volume of steam and thus the distance between the magnetic object 104 and the further magnetic object 103 changes, thereby altering the resonance frequency as the temperature changes.

Fig. 3 shows schematically and exemplarily a further embodiment of the measuring device. The measuring device 201 further includes: a housing 202; a magnetic object 204 disposed within the housing 202 such that if an external magnetic moment acts on the magnetic object 204, the magnetic object may rotate out of an equilibrium orientation; and a reset torque unit 203 comprising another magnetic object 203. Also in this embodiment, in the equilibrium orientation of the magnetic object 204, the magnetic dipole of the magnetic object 204 and the magnetic dipole of the further magnetic object 203 are directed in opposite directions. Another magnetic object 203 is attached to the end face of the housing 202 by using, for example, glue 209. In this embodiment, the measuring element adapted to change the resonance frequency depending on the temperature comprises a lever structure 213 via which lever structure 213 the magnetic object 204 is attached to the housing 202, wherein the lever structure 213 comprises a material which changes its length depending on the temperature such that the distance between the magnetic object 204 and the further magnetic object 203 and the resonance frequency changes with the temperature.

Fig. 4 shows schematically and exemplarily an embodiment of a reading system for reading a measuring device. In this example, the subject 40 is located on a support device 41 (e.g. a patient table), wherein the coils 42 are integrated in the support device 41. The coil 42 may also be disposed in another manner proximate the subject 40. For example, they may be integrated in a mat that can be placed on the support means 41. The measurement device 1 has been introduced into the subject 40 in order to measure the pressure in the subject 40.

The coil 42 is adapted to a) generate a magnetic field providing a magnetic moment for rotating the magnetic object 4 of the measuring apparatus 1 out of its equilibrium orientation and for thereby exciting a rotational oscillation of the magnetic object 4 such that it oscillates at a resonance frequency, and b) generate an induced signal caused by the rotational oscillation of the magnetic object 4. The reading system further comprises a control unit 43 configured to control the coil 42 by providing and controlling a current for the coil 42 such that a desired magnetic field is generated, and to generate a digital induction signal indicative of an inductive influence caused by the rotational oscillation of the magnetic object 4 of the measuring device 1 on the current in the coil. The coil 42 and the control unit 43 magnetically excite the measuring device 1 and generate an induced signal, such that the coil 42 and the control unit 43 can be considered to form the excitation and

induction signal unit

42, 43.

Although in this embodiment the same coils are used for generating the magnetic field and for generating the induction signal, in other embodiments it is also possible that a) a first coil is used for generating the magnetic field, which provides the magnetic moment, for rotating the magnetic object 4 of the measuring device 1 out of its equilibrium orientation and for thereby exciting a rotational oscillation of the magnetic object 3, and b) a second coil is used for generating the induction signal, wherein the first and second coils are separate.

The reading system further comprises a determination unit 44 adapted to determine a temperature or other physical or chemical quantity based on the generated sensing signal. In particular, the reading system is adapted to provide magnetic fields at different excitation frequencies, wherein the excitation frequency at which the generated induction signal indicates a maximum induction is determined and the determined excitation frequency is regarded as the resonance frequency. Furthermore, the determination unit 44 may comprise a predetermined allocation between a) the resonance frequency and b) the temperature or other physical or chemical quantity, respectively, and use this allocation together with the currently measured resonance frequency to determine the temperature or other physical or chemical quantity, respectively.

The reading system further comprises an input unit 45, such as a keyboard, a computer mouse, a touch pad, etc., and an output unit 46, such as a monitor, for outputting the determined temperature or other physical or chemical quantity, respectively.

Next, an embodiment of a measurement method for performing measurement by using the measurement apparatus 1 will be exemplarily described with reference to a flowchart shown in fig. 5.

In step 401, a magnetic field is generated, which provides a magnetic moment for rotating the magnetic object 4 of the measurement apparatus 1 within the subject 40 out of its equilibrium orientation and for thereby exciting the magnetic object 4 into a rotational oscillation such that it oscillates at the resonance frequency of the rotational oscillation of the magnetic object 4. Furthermore, in step 401, inductive signals are generated, which are caused by the rotational oscillations of the magnetic object 4. In particular, magnetic fields with different excitation frequencies, including the resonance frequency, are generated. Thus, although the resonance frequency is initially unknown and should be determined, it is known in which frequency range the resonance frequency will likely lie, wherein a magnetic field is generated having excitation frequencies that cover the known frequency range in which the resonance frequency is expected to lie. In step 402, a temperature or other physical or chemical quantity, respectively, is determined based on the generated sensing signal, and in step 403, the determined temperature or other physical or chemical quantity, respectively, is output.

Steps 401 to 403 may be performed cyclically such that the measurement is performed substantially continuously and output to, for example, a surgeon performing, for example, a surgical procedure, until the measurement is aborted. The measurement may be aborted after an expected stop of the measurement has been indicated to the reading system by the input unit 45.

The measurement device is particularly useful in thermal ablation procedures to control the thermal energy applied to a subject in accordance with a measured temperature. The measurement device preferably has a sub-millimeter size and can be placed in or at the tissue to be ablated in order to monitor the temperature of the tissue during the ablation procedure. The measurement device provides a wireless solution for measuring temperature or other physical or chemical quantities such as pressure so that the measurement device can be delivered to an intended location within the subject's body, e.g. via the bloodstream. The measurement device may be placed, for example, at or within a tumor in order to monitor temperature during tumor resection. The measuring device is not only very small (i.e. sub-millimeter in size), but also extremely sensitive and very accurate, wherein the measuring device can be remotely detected, for example by means of a coil system as described above.

The magnetic material to be used for modifying the temperature dependence of the measuring device as desired (e.g. the

magnetic materials

5, 6 described above with reference to fig. 1) is preferably a low curie temperature material, wherein the magnetic material is also applicable to the embodiments described above with reference to fig. 2 and 3 to tailor the temperature dependence of the resonance frequency as desired. The housing of the measuring device may be, for example, a metal or polymer housing. Furthermore, there may be a gas within the housing or it may also contain a vacuum.

The measuring device preferably comprises two magnetic objects which are rotatable relative to each other, wherein in one embodiment one of the two magnetic objects is fixed to the housing, e.g. by glue, and the other of the magnetic objects is suspended by a filament, e.g. a thin wire or a thread. The oscillation frequency is related to the magnetic field strength at the magnetic objects in the oscillation, preferably spheres, and thus to the distance between the magnetic objects. Thus, by converting the physical or chemical quantity to be measured into a change in distance via a suitable measuring structure, a shift in the resonance frequency can be achieved and used for measuring the physical or chemical quantity. In the case of pressure measurement, the measuring structure (i.e. the measuring element) may simply be a membrane. In the case of using a device for measuring temperature, a measuring element is used which is adapted to increase the natural temperature dependence of the resonance frequency, which is usually not very high. For example, while thermal expansion of the housing may increase the distance between the magnetic objects, thermal expansion of the filaments shortens the distance. Therefore, the total change in the resonant frequency is not very high according to the temperature change. As a measuring element, a filament with a negative length change with increasing temperature can be used, in order to increase the distance between the two magnetic objects as well with increasing temperature. Such filaments may be or comprise carbon fibers or drawn polymer fibers. Preferably, however, the measuring element is an additional element similar to the magnetic material described above. The magnetic material preferably has a curie temperature that is only slightly above the maximum operating temperature of the measurement device. The magnetic material may be applied at many different locations within the measuring device, but preferably the magnetic material is positioned in the vicinity of another magnetic object, which is preferably fixed. Generally, magnetic materials lose magnetization with increasing temperature. However, depending on where the low curie temperature material is located, the effect on frequency is either positive or negative, i.e., as the temperature increases, the frequency shifts either toward higher frequencies or toward lower frequencies. In fig. 1, the magnetic material 6 is a soft magnetic material which is magnetized in the opposite direction compared to the other magnetic body 3 and thus always reduces the field strength at the location of the rotating magnetic body 4. However, the magnetic material 5 has the same magnetization direction as the other magnetic object 3, and thus always increases the field strength and thus the resonance frequency decreases with increasing temperature. Therefore, by using the magnetic material, the direction of the temperature dependence of the resonance frequency and the strength of the temperature dependence can be adjusted as needed. Thus, magnetic materials can be used to compensate for a wide range of detrimental temperature variations. The magnetic material may be an iron-nickel alloy, wherein the curie temperature may be adjusted by the composition of the alloy. However, other low curie point materials may also be used.

The magnetic material may have a curie temperature, for example, 100K or less above the maximum operating temperature of the measurement device. In one embodiment, the curie temperature is 10K above the maximum operating temperature of the measurement device. The magnetic material may also be a combination of several magnetic materials with different curie temperatures (which may be referred to as weak magnetic materials). If the magnetic material is a combination of several weakly magnetic materials, one or more of these weakly magnetic materials may also have a Curie temperature that is lower than the maximum operating temperature.

The maximum operating temperature is related to the application for which the measuring device should be used. It may be equal to or less than 50 ℃ or equal to or less than 100 ℃. In one embodiment, the measuring device is adapted for measuring body temperature only. The maximum operating temperature may be 50 ℃. In the case of ablation monitoring, the maximum operating temperature may be 100 ℃. The maximum operating temperature may be even higher if the measurement device is used in non-medical applications.

The measuring device may also comprise other measuring elements for providing a high sensitivity of the resonance frequency to temperature changes. For example, the vapor pressure of the liquid may be used to actuate a change in distance between the magnetic objects, e.g., as described above with reference to fig. 2. It is also possible that thermal expansion of the material is used together with the lever structure for generating large distance changes with temperature changes, e.g. as described above with reference to fig. 3.

During the measurement, a plurality of measuring devices may be used simultaneously, wherein the plurality of measuring devices are adapted to have respective resonance frequencies in respective frequency ranges when the respective measuring devices are used for the measurement, and wherein the frequency ranges of the different measuring devices do not overlap. This allows the reading system to distinguish between different measuring devices based on the respective resonance frequencies and to determine a respective temperature or other physical or chemical property for each respective measuring device, respectively.

If a measuring device is used for determining the temperature, the measuring element, such as the above-mentioned soft magnetic material, is preferably selected and arranged such that the change of the resonance frequency with temperature is greater than or equal to 10Hz/K, and further preferably greater than or equal to 100 Hz/K. If the measuring device is adapted to measure other physical or chemical properties, the measuring elements are preferably selected and arranged such that the dependence of the resonance frequency on temperature is equal to or less than 1Hz/K, and further preferably less than 0.1 Hz/K.

Although certain embodiments of the measuring device have been described above, other measuring devices may be used, comprising a housing, a rotatable magnetic object, a return torque unit providing a return torque to force the magnetic object back into an equilibrium orientation, and a measuring element adapted to alter the resonance frequency in dependence of temperature and/or in dependence of other physical or chemical quantities, wherein if the measuring element is adapted to alter the resonance frequency in dependence of other physical or chemical quantities, the measuring device comprises a compensating element adapted to alter the resonance frequency in dependence of temperature variations in a first frequency direction, which is opposite to a second frequency direction, if the compensating element is not part of the measuring device, the measuring device will alter the resonance frequency in dependence of temperature variations in the second frequency direction. For example, in one embodiment, the flexible portion 8 of the housing 2 shown in fig. 1 is rigid, and the housing 2 may be partially filled with a liquid that is preferentially adsorbed to solid materials, such that vapour is present within the housing, wherein, in this example, the housing has a certain flexibility such that it changes its length and/or may be arcuate, for example, wherein this flexibility, together with the temperature dependence of the vapour within the housing, may result in a change in the distance between two magnetic objects within the housing, and thus in a shift of the resonance frequency with temperature. It is also possible that in fig. 3 the lever structure comprises more arcs than the one arc 213 shown in the figure in order to improve the temperature sensitivity. Furthermore, it is likewise possible for the restoring torque unit to comprise a torsion spring mechanism for providing the restoring torque in addition to or instead of another magnetic body. For example, a torsion spring may be used instead of the filament 7 shown in fig. 1. It is also possible to use two torsion springs, each connecting the rotating magnetic body 4 with a respective one of the

opposite surfaces

30, 31. Furthermore, it is also possible that in the measuring device the measuring element comprises a magnetic material which is applied to the magnetic body and influences the dipole moment of the magnetic body, wherein the influence of the magnetic material is temperature-dependent in order to change the dipole moment of the magnetic body in the event of a temperature change. Therefore, a magnetic material that changes its magnetization with a change in temperature can also be applied to a rotating magnetic object.

Although in the above described embodiments the measuring device is adapted to measure pressure as other physical or chemical quantities, in other embodiments the measuring device may be adapted to measure other physical or chemical quantities. This may be achieved, for example, by configuring the measuring device such that a change in the expected physical or chemical quantity results in a change in the distance between the magnetic object and the further magnetic object, or more generally in a change in the reset torque provided by the reset torque unit.

One example of another chemical parameter to be measured would be to use a membrane made of a material that changes mechanical properties in the presence of organic solvents in the environment (e.g. natural rubber). If the housing has some kind of hole, i.e. no pressure is measured, the device will give a record of the presence of organic solvent in the environment.

The generation of the magnetic field, which provides a magnetic moment, for rotating the magnetic object of the measuring device out of its equilibrium orientation and for thereby exciting a rotational oscillation of the magnetic object such that it oscillates at the resonance frequency, can be achieved in many different ways. For example, the excitation may use individual pulses of the magnetic field, wherein between the pulses the frequency and phase of the induced signal may be measured. Thus, the timing of the next short pulse can be calculated such that it increases the oscillation amplitude of the magnetic article. Alternatively, the single pulse may be replaced with a pulse train consisting of several pulses with positive and negative amplitudes. The short pulse train still covers a relatively wide potential excitation spectrum, which is designed to be centered approximately at the desired resonance frequency. The timing of the pulse train is adjusted again so that it increases the oscillation amplitude of the magnetic object. The frequency of the obtained optimized induced signal can be considered as the resonance frequency.

In an embodiment, the reading system may further be adapted to generate sensing signals which are related to the spatial position of the measuring device and optionally also to the orientation of the measuring device, wherein the determination unit may be adapted to determine the position of the measuring device and optionally also the orientation of the measuring device based on the generated sensing signals. In particular, the spatial sensitivity profiles of the individual coils can be used to determine the position and optionally also the orientation of the measuring device.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The processes performed by one or several units or devices, such as determining the temperature or other physical or chemical quantities, controlling the excitation of one or several measuring devices by controlling the current in the coil, etc., may be performed by any other number of units or devices. These procedures and/or the control of the reading system according to the measuring method can be implemented as program code means of a computer program and/or as dedicated hardware.

A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems.

Any reference signs in the claims shall not be construed as limiting the scope.

The invention relates to a measuring device comprising a rotatable magnetic body which can oscillate at a resonant frequency when excited by an external magnetic moment. The measuring device is adapted to relate the resonance frequency to temperature or to another physical or chemical quantity, such as pressure, in order to allow a wireless temperature measurement or a wireless measurement of another physical or chemical quantity via an external magnetic field providing an external magnetic moment. The measuring device may be relatively small, readable over a relatively large distance, and allow very accurate measurements to be made.

Claims

1. A measurement device, comprising:

a housing (2; 102; 202),

a magnetic object (4; 104; 204) arranged within the housing (2; 102; 202) such that the magnetic object can be rotated out of an equilibrium orientation with an external magnetic moment acting on the magnetic object (4; 104; 204),

-a reset torque unit (3; 103; 203) adapted to provide a reset torque to force the magnetic object (4; 104; 204) back into the equilibrium orientation in case an external magnetic moment has rotated the magnetic object (4; 104; 204) out of the equilibrium orientation, so as to allow a rotational oscillation of the magnetic object (4; 104; 204) at a resonance frequency excited by the external magnetic moment, and

-a measuring element (5, 6; 8; 113; 213) adapted to modify the resonance frequency depending on a) temperature and/or b) pressure or the presence of an organic solvent,

wherein, in case the measuring element (8; 113; 213) is adapted to modify the resonance frequency in dependence of pressure or the presence of an organic solvent, the measuring device comprises a compensation element (6) adapted to modify the resonance frequency in a first frequency direction in dependence of a temperature change, the measuring device will modify the resonance frequency in a second frequency direction in dependence of the temperature change, the first frequency direction being opposite to the second frequency direction, if the compensation element (6) is not part of the measuring device.

2. The measuring device according to claim 1, wherein the reset torque unit (3; 103; 203) comprises: a further magnetic object (3; 103; 203) for generating a magnetic field at the location of the magnetic object (4; 104; 204) such that the reset torque unit provides the reset torque; and/or a torsion spring mechanism for providing the return torque.

3. The measuring device according to claim 2, wherein the measuring element (5, 6; 8; 113; 213) is adapted such that the strength of the magnetic field generated at the location of the magnetic object (4; 104; 204) and/or the dipole moment of the magnetic object (4; 104; 204) changes with a) temperature and/or b) other physical or chemical quantities.

4. A measuring device according to claim 3, wherein the measuring element comprises a magnetic material (5, 6) influencing the magnetic field generated by the further magnetic object (3), the influence of the magnetic material (5, 6) being temperature dependent in order to change the magnetic field strength at the location of the magnetic object (4) in case of a change in the temperature.

5. The measuring device according to claim 4, wherein the magnetic material (5, 6) is arranged adjacent to the further magnetic object (3).

6. The measuring device according to any one of claims 4 and 5, wherein the magnetic material (5, 6) is adapted such that its magnetization decreases with increasing temperature.

7. Measuring device according to any of claims 3 to 6, wherein the measuring element (8; 113; 213) is adapted such that the distance between the magnetic object (4; 104; 204) and the further magnetic object (3; 103; 203) changes if the temperature and/or if the other physical or chemical quantity changes, in order to change the magnetic field strength at the location of the magnetic object (4; 104; 204).

8. The measurement device according to any one of claims 3 to 7, wherein the measurement element comprises a magnetic material which is applied to the magnetic object and influences the dipole moment of the magnetic object, the influence of the magnetic material being temperature dependent so as to change the dipole moment of the magnetic object in case of a change in the temperature.

9. The measuring device according to any one of the preceding claims, wherein the compensating element (6) comprises a magnetic material which changes its magnetization with temperature and thereby the resonance frequency, the magnetic material being selected and arranged within the measuring device such that the direction of change of the resonance frequency is the first frequency direction.

10. The measuring device according to claim 9, wherein the magnetic material is arranged adjacent to the magnetic object (4).

11. The measurement device according to claim 9 when dependent on claim 2, wherein the magnetic material is arranged adjacent to the further magnetic object (3).

12. A kit of a plurality of measuring devices according to any preceding claim, wherein each measuring device is adapted to have the resonant frequency in a respective frequency range when the respective measuring device is used for measurement, the frequency ranges of different measuring devices not overlapping.

13. A reading system for reading a measuring device according to any one of claims 1 to 11, wherein the reading system comprises:

-an excitation and induction signal unit (32, 33) adapted to: a) generating a magnetic field, which provides a magnetic moment, for rotating the measuring device (1; 101, a first electrode and a second electrode; 201) the magnetic object (4; 104; 204) is rotated out of its equilibrium orientation and is used to thereby excite the magnetic object (4; 104; 204) such that the magnetic object oscillates at the resonant frequency; and b) generating an induction signal, which is generated by the magnetic object (4; 104; 204) is caused by the rotational oscillation of the rotor,

-a determination unit (34) adapted to determine a temperature or a pressure or a presence of an organic solvent based on the generated sensing signal.

14. A measuring method for performing a measurement by using a measuring device (1; 101; 201) according to any one of claims 1 to 11, wherein the measuring method comprises:

-generating a magnetic field providing a magnetic moment for rotating the magnetic object (4; 104; 204) of the measuring device (1; 101; 201) out of its equilibrium orientation and for thereby exciting a rotational oscillation of the magnetic object (4; 104; 204) such that it oscillates at the resonance frequency, and

receiving a generated induced signal caused by a rotational oscillation of the magnetic object (4; 104; 204),

15. A computer program comprising program code means for causing a reading system as defined in claim 13 to carry out the steps of the measuring method as defined in claim 14, when the computer program is run on a computer controlling the reading system.